Gun-barrel rifling

ABSTRACT

THE RIFLING OF A GUN BARREL CONSISTS OF THREE PERIPHERALLY EQUISPACED SHALLOW HELICAL GROOVES SEPARATED BY LANDS OF SAWTOOTH-SHAPED PROFILE WITH AN APEX ANGLE OF APPROXIMATELY 90* TO DEFINE A GENERALLY RADIAL GUIDING EDGE FACING IN THE DIRECTION OF TWIST AS VIEWED WHEN LOCKING TOWARD THE MUZZLE. THE BOTTOM OF EACH GROOVE, CENTERED ON THE BARREL AXIS, EXTENDS OVER AN ARC OF SUBSTANTIALLY 90* AND MERGES TANGENTIALLY INTO THE RISING CLAMP OF THE ADJOINING SAWTOOTH.

Nov. 2, 1971 K. BURGSMULLER 3,616,562

4 GUNBRREL RIFLING 2 Sheets-Sheet l PR/OR ART Nov. 2,1971 K. BU'RGSMULLER GUNBARREL RIFLING 2 Sheets-Sheet 2 Filed Sept. 2, 1969 Karl BurgsmUl/er IN VliN'/ UR.

Attorney 3,616,562 GUN-BARREL RHFUNG Kari llurgsmiiller, Finns Hainherg, 335 Kreiensen, Germany Filed Sept. 2, i969, Ser. No. 354,565 lint. Cl. Edic 2] /00, 21/04 US. Cl. i2-70 6 'Claims ABSTRACT F THE DES'CLSURE The riiling of a `gun barrel consists of three peripherally equispaced shallow helical grooves separated by lands of sawtooth-shaped prole with an apex angle of approximately 90 to deiine 'a generally radial guiding edge facing in the direction of twist as viewed when looking toward the muzzle. The bottom ot each groove, centered on the barrel axis, extends over an arc of substantially 90 and merges tangentially into the rising flank of the adjoining sawtooth.

My present invention relates to the riding of a gun barrel.

Conventional riling takes the form of a plurality of angularly equispaced shallow peripheral grooves which are helically twisted, e.g. at a rate of three turns over an axial length of 100 calibers, and which are separated by lines of trapezoidal prole. Usually, there are four such lands spaced 90 apart.

The trapezoidal outline of each land, with flanks converging toward the barrel axis, is designed to allow these lands to bite into the outer surface of the projectile in order to set it in rotation about the barrel axis as the projectile advances toward the muzzle. One of the flanks of each land, i.e. the one facing in the direction of twist as viewed when looking toward the muzzle or discharge end of the gun barrel, acts as an active guiding edge imparting the desired spin to the projectile; in so doing, this edge exerts upon an outer peripheral zone of the projectile an oblique force with a major tangential component and a minor radial component, the latter tending to compress the material of the projectile (or of its surrounding steel band) and giving rise to a reaction force which considerably increases the friction between the projectile and the gun barrel. This radial stress also tends to expand the bore of the gun barrel, particularly along its weakest points so as to accentuate its almost invariably present initial eccentricity and to distort its shape. Since the tangential component must overcome the rotative inertia of the projectile, a certain compression also occurs in the peripheral direction along the active guiding edge whereby an air gap tends to develop at the opposite passive edge. This air gap, present at each of the several lands, provides a leakage path for the escape of propellant vapors whereby the eiiiciency of the firing is diminished. The escaping vapors also entrain metal particles detached from the projectile body which are apt to become imbedded in the peripheral surface of the gun barrel, thereby contaminating same and impairing its performance. Finally, if the angle of inclination of the active edge with reference to the radial direction is greater than the angle of friction between the gun barrel and the projectile, the camming action due to the relative rotation of these bodies generates an outward force augmenting the distortion-inducing stress.

The `general object of my invention is to provide an improved gun barrel avoiding the aforestated disadvantages.

More specifically, it is an object of my invention toproivide a gun-barrel profile of such configuration as to minimize the aforementioned distortion-inducing 3,0%,502 Patented Nov. 2 197i force7 thereby reducing the internal friction and virtually eliminating any radial distension of the bore.

Another important object is to provide an improved form of riing insuring positive guidance and centering even with a reduced number of lands, specifically three lands spaced 120 apart to afford accurate three-point support for the projectile.

These objects are realized, pursuant to my present invention, by the provision of a rified gun barrel whose lands are of sawtooth-shaped prole with a generally radial guiding edge facing in the direction of twist as delined above.

Advantageously, the apex angle of the sawtooth, i.e. the angle included between this guiding edge and the rising sa'wtooth Hank, is approximately 90, the guiding edge including an obtuse angle of less than with the bottom of the adjoining groove. In a preferred embodiment this obtuse angle is substantially 95 whereby the guiding edge includes an angle of about 5, well below the angle of friction, with a radial plane passing through the root of this edge.

According to another advantageous feature of my invention, the rising flank of the sawtooth is a curve (eg. a section of an Archimedian spiral or a parabola) merging tangentially into the circularly arcuate bottom of the adjoining groove. With three such lands spaced apart, pursuant to the preferred embodiment, the profile of this groove bottom advantageously extends over an arc of about 90 so as to correspond substantially to a quadrant of a circle centered on the barrel axis, the arc length of the incurved sawtooth flank being then approximately equal to 30.

The invention will be described in greater detail hereinafter with reference to the accompanying drawing in which:

FIG. l is a cross-sectional view of a conventional gun barrel and a projectile engaged by its riiling;

FIG. 2 is a view similar to FIG. 1 but showing my improved gun barrel; and

FIG. 3 is an enlarged detail view of the region designated III in FIG. 2.

In FIG. 1, I have shown a gun barrel 11 and a projectile 12 guided therein. The generally cylindrical bore of the barrel, centered on an axis O, is formed with four angularly equispaced grooves 13 separated by as many lands 14 of substantially trapezoidal outline. Each land forms an active edge X and a passive edge Y which are Igiven the usual right-handed twist so as to impart clockwise rotation to the projectile 12 as the latter is propelled toward the muzzle, i.e. away from; the observer as Iviewed in FIG. 1. Each of the -anks X and Y includes with a radial plane R, passing through the root of the flank as well as through the axis O, an angle of about 35. The extensions of these anks define a square with an inscribed circle C whose radius is a. major fraction of the bore radius.

The radial and tangential force components effective at the active edge X, as described above, give rise to respective reaction forces K1 and KZ with a resultant K. Force K1 tends to expand the barrel 11 and also generates considerable friction which requires the use of relatively slow-burning powders to accelerate the projectile. Some of the resulting vapors iind an escape path at an air gap A of rhomboidal shape developing at the passive edge Y.

I shall now describe, with reference to FIGS. 2 and 3, the improved gun barrel embodying my invention.

The gun barrel ll shown in FIG. 2 has a riiled internal profile formed from three shallow grooves 2 with intervening lands 4l of sawtooth-shaped outline. As best seen in FIG. 3, each of these lands has a generally radial guiding edge 3 dening an angle of 5 with a radial plane R passing through the root 7 of that edge. Thus, the obtuse angle included at the root 7 between the edge 3 and the bottom of the adjoining groove 2 is 95.

At the apex 5 of the sawtooth profile, edge 3 meets the rising iiank S of the sawtooth at a right angle, this flank merging tangentially into the bottom of the opposite groove 2 at a point 6 which is 90 away from the root point 7 of the next land d. Thus, the bottom of groove 2 forms a circular quadrant, centered on barrel axis O', between points 6 and 7, the incurved tiank 8 extending over an arc of 30. A circle C tangent to the extensions X of all edges 3 has a diameter which is only a small fraction of the bore diameter.

Owing to the small slope and curvature of fianks 8, any relative rotary displacement between the gun barrel 3l and a projectile resisting the tangential force exerted by guiding edges 3 will not give rise to an appreciable clearance between the projectile surface and the flanks 8 so that virtually no propellant fumes can escape and no extraneous metallic particles will become lodged in the bore wall. Though the slope of edge 3 is sumcient to center the projectile, no appreciable radial force component will be generated thereby. With angle ,8' substantially less than the angle of friction between the projectile and the gun barrel, the bore-distorting force will be negligible elven if the axes of the barrel and its bore do not precisely coincide. Thus, the height of the lands may be significantly reduced in comparison with conventional proles as illustrated in FIG. i, despite the decrease in the number of lands from four to three. The combined effect of this decrease in the number of lands, the change in land profile and the reduction in land height is an enlargement in the effective cross-sectional area of the projectile by a major fraction of 1% (at least 0.6% in the specific case here considered). The re* sulting increase in propulsive force, along with the afore described diminution of friction, entails a more efficient use of the available propellant.

I claim:

l. A rifled gun barrel provided internally with a plurality of helically twisted shallow peripheral grooves defining a like number of intervening lands of sawtoothshaped profile angularly equispaced about the barrel axis, each of said lands having a generally radial guiding edge facing in the direction of twist of said grooves as viewed when looking toward the discharge end of the gun barrel, each of said grooves having an arcuate bottom centered on said axis and extending over an arc exceeding by several times the peripheral width of any of said lands.

2. A gun barrel as defined in claim l wherein said sawtooth-shaped profile has a rising ank extending substantially at right angles to said guiding edge.

3. A gun barrel as defined in claim 2 wherein said guiding edge includes with the bottom of the adjoining groove an obtuse angle of less than 1100.

4. A gun barrel as defined in claim 3 wherein said guiding edge includes an angle of about 5 with a radial plane passing through the root of said guiding edge.

5. A gun `barrel as defined in claim 2 wherein said rising fiank is a curve merging tangentially with the bottom of the adjoining groove.

6. A gun barrel as defined in claim 5' wherein said lands are spaced apart, the bottom of each groove having a cross-section substantially corresponding to a quadrant of a circle centered on the gun-barrel axis, said rising ank extending over an arc of substantially 30.

References Cited FOREiGN PATENTS 14,271 1852 Great Britain 42--78 BENJAMIN A. BORCHELT, Primary Examiner J. M. HANLEY, Assistant Examiner 

